Primary Forests: Why They Matter for Climate, Water and Biodiversity
In the face of climate change and biodiversity loss, primary forests are irreplaceable ecosystems. They support exceptional biodiversity, hold vast carbon stocks and contribute to the functioning of water and soil cycles.
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What are primary forests and where are they found?
According to the FAO definition, a primary forest is a naturally regenerated forest of native tree species where there are no clearly visible indications of human activities and ecological processes are not significantly disturbed. This is more nuanced than the idea of a forest that has “never been touched” by people. FAO guidance can include forests where traditional stewardship takes place without significantly disrupting ecological processes, as well as forests where old human interventions occurred long enough ago for natural composition and dynamics to become re-established.
Today, these forests remain exceptionally valuable and continue to decline globally.
It is important to distinguish primary forest from tropical forest. The word “tropical” refers mainly to climate and geographical zone, whereas “primary” describes ecological condition and human disturbance. In other words, a primary forest is not necessarily a tropical forest. Primary forests also exist in boreal and temperate regions.
The map below provides an older representation of the distribution of primary forests (dark green) and their historical distribution (light green). For the latest figures, FAO’s Global Forest Resources Assessment 2025 estimates that at least 1.18 billion hectares of primary forest remain worldwide, around 29% of global forest area. Russia, Brazil and Canada together contain about 62% of the reported global primary-forest area. These data underline the scale of primary-forest loss in recent history, although trends differ greatly between regions.
👉 Source: Klorane Botanical Foundation
Biodiversity and carbon storage
Primary forests are home to extraordinary biodiversity. Their long ecological continuity and natural regeneration processes can create high structural complexity, providing habitat for many species, including organisms that depend on old trees, dead wood, stable microclimates or long-established ecological relationships.
Carbon is another major issue. Primary forests can hold considerable stocks in living biomass, dead wood and soils, and protecting them also avoids some of the emissions associated with degradation and deforestation. Forests are among the planet’s major terrestrial carbon stores and sinks. Their climate role is not limited to tree growth: soil integrity, dead wood, stand diversity and preservation of the ecosystem as a whole also matter.
Water and wellbeing
Research on forest hydrology shows that forests that are primary or long-established can influence infiltration, runoff and aquatic habitats . Canopy, litter, roots and forest soils affect how rainfall reaches the ground, infiltrates and moves towards streams. These effects vary with climate, topography, soil and forest type, so it is too simplistic to say that every forest systematically “cleans” water or always increases groundwater recharge. Trees also take up water through their roots and return some of it to the atmosphere through transpiration, contributing to the water cycle.
Many studies also suggest that exposure to forest environments may be associated with benefits for physical and mental wellbeing, through mechanisms that may include relaxation, gentle physical activity and changes in stress-related markers. Depending on study design and population, research has reported lower perceived stress or favourable changes in some physiological measures, although spending time in forests is not a medical treatment in itself. A simplified POMS-based worksheet (Profile of Mood States), adapted as a non-diagnostic reflection tool for my forest therapy practice, is also available on my website to help participants observe how they report feeling before and after a nature experience.
Existe t-il des forêts primaires en France ?
According to the latest results from France’s National Forest Inventory published by IGN, mainland France and Corsica contain around 17.7 million hectares of forest in 2026. In mainland France, primary forest meeting the strict FAO-style criteria is generally considered to have disappeared. That does not mean there are no ancient forests, old-growth stands or forests with high naturalness: these concepts are different. French Guiana, by contrast, retains vast areas of primary forest.
In mainland France, attention can instead turn to ancient forests, old-growth stands and forests left to develop with little or no harvesting. A study highlighted by INRAE estimated that around 3% of French forests had not been harvested for at least 50 years. Over time, some signs of management fade and natural dynamics regain space, but this does not automatically make these forests “primary” in the strict sense. Forests developing without recent harvesting can nevertheless be valuable for biodiversity, dead wood and the study of natural forest dynamics.
Between Nantes and Angers, the Pays d’Ancenis offers beautiful wooded natural areas. Why not discover them during one of the public forest therapy walks I lead in the Pays d’Ancenis and surrounding area (see the Events and Forest Therapy Training section)?
I also offer gift cards for forest therapy experiences. They can be a lovely way to share a memorable moment with a friend or family member.
See you soon!
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